With the burgeoning use of the personal computer and computer workstation, it has become increasingly important to the users of such computers to have convenient control of the cursor on the computer's video display.
The simplest form of cursor control for such computers involves the use of cursor keys, typically located on the keyboard for the computer. However, use of the cursor keys tends to give only very slow and awkward performance. An alternative to the cursor keys is the light pen, which uses a light beam on a special reflective surface to move the cursor.
A more recently developed cursor control device is the electronic mouse. Electronic mouse come in two general types. The first type uses reflection of a light beam off a coded surface to control cursor movement. The more versatile, and more popular, mouse, such as the Logitech C7 mouse manufactured by the assignee of the present invention, provides optomechanical operation which requires nothing more than a flat surface over which the mouse can be rolled. Such electronic mice comprise a case held in the hand. In the bottom of the case is a frictional ball. Cursor movement is controlled by holding the case in the hand such that the ball engages the flat surface. The ball also frictionally engages shaft encoders which convert the analog movement of the ball into digital cursor control. One of the limitations of electronic mice, however, is that they have needed a flat surface of at least several square inches to be used. Such surface area is not always available, and so an electronic mouse is not a solution in all situations.
Another cursor control device is the trackball. Trackballs, while similar to electronic mice, differ in some very significant respects. While mice typically have cases formed to be held in the hand, and thus have relatively small rolling balls, trackballs are designed to have the case remain stationary, with only the ball being rotated. Thus, the ball is markedly larger than for an electronic mouse. In addition, the ball for a mouse must smoothly engage the surface over which it rolls, and thus is typically coated with rubber or similar polymer, and is weighted to ensure good frictional engagement. A trackball, on the other hand, is controlled by direct contact with the hand, and thus needs no such coating since finger pressure can be varied to ensure frictional engagement.
One of the difficulties with trackballs in the past has been that the cases of such trackballs were large, to accommodate the large ball needed for convenient hand movement. In addition, conventional trackballs typically have been intended for use within only a very narrow range of elevational angles, and could not be used in, for example, the inverted position. As the result of these and other limitations, the trackball has been primarily intended as a stationary cursor control device.
There has therefore been a need for a cursor control device which can be used in very limited space, and yet still be capable of reliable operation over a wide range of elevational angles, such as might be encountered in using a laptop computer.